With the second round of nuclear talks between Iran and the six major powers due to begin in Tehran on Wednesday, senior Israeli sources say Jerusalem may be more flexible about Iranian low-level uranium enrichment than it is currently willing to let on.

Though Israel has been expressing zero flexibility regarding a possible deal with Iran, Defense Minister Ehud Barak a few weeks ago issued a written statement that Israel would consent to Iran's continuing enrichment of uranium to a low level of 3.5 percent, as well as to allowing a few hundred kilograms of 3.5-percent enriched uranium to remain in that country.

"Enrichment percentage" refers to the degree to which natural uranium has been enriched with the U-235 isotope - an isotope which can sustain a chain reaction of nuclear fission. Reactor-grade uranium is enriched to about 3 to 4 percent, while weapons-grade uranium is 90 percent enriched. However, crude nuclear weapons can be built with uranium enriched to as low as 20 percent.

A senior Israeli source said that Barak's remarks, which were shared in private conversations with U.S. officials, contradict the tough line being presented by Prime Minister Benjamin Netanyahu, who has demanded that Iran stop all uranium enrichment and give up any enriched uranium it has in its possession.